Fungal organisms have become increasingly significant pathogens in immunocompromised patients, especially those who because of cancer, organ transplantation, chemotherapy, pregnancy, age, diabetes, complications following extensive surgery, and various immune system dysfunctions, are at risk of experiencing life-threatening diseases caused by organisms which do not ordinarily pose a threat to normal, immunocompetent people. For example, fungal infections have become one of the leading factors contributing to morbidity and mortality in cancer patients, and fungi account for 4-12% of nosocomial (hospital-acquired) pathogens in leukemia patients (E. Anaissie, Clin. Infect. Dis., 14Suppl.1!:S43 1992!). The incidence of nosocomial bloodstream infections with fungi such as Candida ("candidemia") has increased in recent years and now accounts for 5.6% of all primary bloodstream infections (Id.). Yeast infections may also be life-threatening in other settings, such as in the case of intravenous drug abusers who use non-sterile substances (lemon juice is commonly used) to dilute drugs prior to injection.
Of the over 100 Candida species, approximately seven are isolated with great frequency from human specimens (T. Mitchell, in Zinsser Microbiology, W. K. Joklik, et al., eds!, Appleton, Century-Crofts, Norwalk, Conn., pp. 1183-1190 1984!). A brief taxonomic chart of Candida is shown in Table 1. Some Candida species are related to organisms, such as Saccharomyces in the subclass Hemiascomycetidae, class Ascomycetes, subdivision Ascomycotina, division Ascomycota. Also, some mycologists consider C. stellatoidea to be a variant of C. albicans.
TABLE 1 ______________________________________ TAXONOMY OF THE GENUS CANDIDA ______________________________________ Kingdom: Mycetae (Fungi) Division: Deuteromycota Subdivision: Deuteromycotina Form Class: Deuteromyces Form Subclass: Blastomycetidae Genus: Candida Species: albicans glabrata guilliermondi krusei lipolytica lusitaniae parapsilosis pseudotropicalis rugosa stellatoidea tropicalis ______________________________________
The first exposure to fungi experienced by many humans occurs during the birth process, when C. albicans present in the mother's vaginal canal colonizes the buccal cavity, and portions of the upper and lower gastrointestinal tract of the newborn. This colonization usually results in the establishment of C. albicans as a commensal organism in these areas, for the life of the individual. However, C. albicans is also the most common fungal pathogen of humans, worldwide, with other Candida species becoming increasingly important in fungal disease in humans and other animals.
As a commensal, C. albicans exists as a unicellular yeast; during invasive disease, the organism has a filamentous morphology. When C. albicans is implicated in disease, it may indicate that the patient has a co-existing immune, endocrine or other debilitating disorder that must also be addressed in order to effectively manage the fungal disease. The principal risk factors that predispose individuals to deeply invasive candidiasis include protracted course of broad spectrum antimicrobials, cytotoxic chemotherapy, corticosteroids, and vascular catheters.